Technical Field
The present invention relates generally to a method for improving the signal to noise ratio of a waveform and, more particularly, to a method for improving the signal to noise ratio of an EEG signal.
Description of Related Art
In many situations, it is desirable to monitor electroencephalography (EEG) signals. For example, hospitals and other medical facilities often utilize EEG monitors to monitor the EEG signals. Additionally, in military applications it is oftentimes desirable to monitor the EEG signals of warriors in a combat arena.
It is well known that under certain circumstances, the human brain responds to certain stimuli in a manner that yields a large-amplitude response with a latency of approximately 300 milliseconds. This signal, known as the P300 response for EEG signal analysis, is considered to be one of the most important EEG signals when assessing the reaction of the brain to a stimulus. Furthermore, even though the P300 response begins around 300 milliseconds following the stimulus for most individuals, the P300 response actually extends between 300 and 600 milliseconds after the stimulus, and is highly variable across individuals and circumstances.
One difficulty in monitoring EEG signals such as the P300 response, however, is that such signals are relatively noisy and, thus, difficult to properly analyze. Indeed, in some situations the signal noise may obscure the P300 EEG waveforms to such a degree that it is difficult to identify or accurately analyze the P300 signal.
There have been previously known attempts to apply noise filtering to the EEG signal in an attempt to improve the signal to noise ratio of the EEG signal and, in particular, the P300 response. These previously known attempts to improve the signal to noise ratio, however, have always focused on applying a static noise filter to sequential time segments of the EEG signal over the entire duration of the signal e.g. 300-600 milliseconds. A disadvantage of this approach, however, is that the noise present on the P300 response signal varies over time even as short as 300 milliseconds-600 milliseconds. Thus, while the noise filter of these previously known methods may improve the signal to noise ratio of the EEG signal over a portion of the 300-600 millisecond time period, they provide minimal, if any, improvement of the signal to noise ratio over other portions of the 300-600 millisecond P300 signal.